Prehistoric tale of the tail evolves at the Royal BC Museum

A Victoria researcher has helped to fill in the gaps in a dinosaur ‘tail’ as old as time.

Royal BC Museum paleontologist Victoria Arbour and Lindsay Zanno of the North Carolina Museum of Natural Sciences set out to understand why two armoured species – separated by more than 300 million years of evolution – developed similar-looking weaponized tails.

Both Glyptodonts – a group of extinct armadillo-like mammals — and Ankylosaurs – large dinosaurs – have unusual clubbed “sledgehammer-like” tails, most likely used “as weapons of intra-specific combat or inter-specific defense.”

“That’s a really weird structure to evolve,” Arbour told Black Press Media. “It’s a really uncommon kind of weapon. So I was really interested in learning a bit more about why these two groups evolved such a similar structure.”

Ankylosaurs and glyptodonts both evolved similar armoured bodies with weaponized tails, but they were separated by over 300 million years.

Using statistical modeling and data about the two animals’ anatomy, the researchers found evidence for strong ‘convergent evolution’ – the process of unrelated groups of animals evolving similar looking body shapes. It usually means “similar selective pressures have shaped their bodies over time” according to Arbour.

Specifically, the two animals became large and herbivorous before evolving the rare tail weapons, and developed stiff tails before the tip was enlarged into a wrecking-ball-like structure.

“We showed that the way in which they evolved their tail club over time was actually really similar,” Arbour said. “We found that they were really strongly convergent, more than we expect [to happen] by chance.

The researchers speculate that ‘tail weapons’ are rare because of the stiff backbone needed to carry them.

“It seems like there’s just kind of a cascade of features that have to be in place for this thing to evolve,” said Arbour. “And understanding why that is, is still unresolved.